METEOROLOGY. 



[THE FATA MOROAXA. 



dcncy to fly from the perpendicular still remaining, this plane. Occasionally, however, the reduplication of 



H manifest.-.!, nut under tin- i-omlition of i 

 I'ut rvllection ; consequently, the ray h m is directed 

 towards the eye of the observer, and, along with tlio 

 other rays upon which a similar operation has !! 

 effected, gives rise to the appearance of an inverted 

 object. In order that the phenomenon should occur, 

 however, there must bo the following conditions besides 

 those already mentioned : Not only must the solar lir.it 

 be considerable, but the air must be calm, so that the 

 lower atmospheric layers may retain a density less con- 

 siderable than the density of those above them. 



As, under the peculiar circumstances just mentioned, 

 refraction may pass into reflection, and the reflection 

 be excited upwards from below, so may the operation be 

 reversed ; in which case the inverted images of terrestrial 

 objects will be seen in the air. The celebrated fata mor- 



IV. Mi 



gana, sometimes observed on the Culahrinu coast, and 

 more especially at Keggio, is a celebrated example of this 

 kind. At certain times, the whole city of Messina and 

 its environs, are reflected downwards from an upper 

 stratum of the air thus presenting an appearance suffi- 

 riently curious, but by no means the striking and well- 

 defined character which the records of early travellers 

 would lead us to suppose. (See Fig. 54). 



Tin- I between atmospheric refraction and 



iion, and, at the same time, a rationale 

 of the jH'vuliar ai ; rial visions which may occur in certain 

 atmospheric states, is furnished by the diagram (Fig. . r >."> , 

 suggested by M. Biot. The line b t c is supposed to be 

 * ray of light proceeding from 6, passing thence down- 

 wards to the point r, whence it in reflected to the ob- 

 server's eye at c. Now the optical conditions of this 

 arrangement are such, that any rays proceeding from '< 

 below the ray 6 ( e represented, would be invisible to the 

 observer at c, whilst two images will be seen of all objects 

 above this line. Supposing the object in question to be 

 a man suppose, further, the man to be wall 

 the observer, he would be presented to the hitter under 

 the successive forms seen in Fig. 65. 



Fift. M. 



image has been projected on vertical planes, of which 

 phenomenon the following is an example. On .luno 

 J'th, 1820, whilst MM. Soret and Turine were in the 

 second storey of a house on the lake of Geneva, they 

 looked towards a ship two miles off, and making for the 

 harbour. Immediately the vessel in question an 

 q (Fig. 50), she appeared reduplicated on a vertical plane ; 

 when she came to r the reduplication still continued, 

 but the second image was further removed than before, 

 and both were distorted ; lastly, when the vessel arrived 

 at the point*, the reduplicated image had receded to a 

 distance still farther away, and both images, though dis- 

 torteil, presented an appearance of distortion very 

 iliil'erent from before'; they were apparently drawn out, 

 elongated both as to the hull and rigging, as 

 in the diagram (Fig. 56). The following is the ex- 

 planation of the phenomenon, as sug- 

 gested by the two observers above- 

 mentioned ; and there seems no reason 

 to doubt its correctness. 



The letters, ABC, represent an 

 outline of the eastern bank of the 

 lake of Geneva ; the air over that 

 2*\ bank had, at the time of observation, 

 -:-J been long under the shadow thrown 

 upon it by the mountains of Savoy, 

 whilst, contemporaneously, the w. 

 bank had been strongly Mated by the 

 sun ; hence, from the conjoint opera- 

 tion of these two causes, there were 

 two vertical layers of atmosphere of 

 different temperature, and consequent- 

 ly of different densities ; hence, they 

 were of two different refractive and re- 

 flective powers. 



All that is necessary to determine 

 aerial reflections, is a sufficient differ- 

 ence between the temperatures of any 

 two adjacent atmospheric layers. In 

 the instance already mentioned, tliis 

 difference had been occasioned by poi - 

 t ons of the ground being hotter th;.n 

 the strata of air 'with which they were 

 in contiguity. The reverse of ti 

 conditions may, however, obtain, and fantastic atmo- 

 spheric delusions may be the result. This latter 

 generally presents itself at sea, and by no means ex- 

 clusively in warm localities. Thus, fur instance, it is 



Fig. 56. 



In tlicw atmospheric optical delusions, involving the 

 appearance of two images, one of them inverted, both 

 natural and inverted image* have occupied a horizontal 



prevalent enough in the Northern Ocean. Sometimes 

 the atmospheric delusion has merely the effect of pro- 

 longing the appearance of an object really below the 

 horizon ; sometimes not only is the appearance pro- 

 longed, but the body is seen double. Whatever the 

 appearance, the atmospheric delusions now under con- 

 sideration are usually seen near the horizon a position 

 w here the optical powers of the atmosphere attain their 

 greatest intensity (Fig. 57). 



THF. RAINBOW. The most beautiful of all luminous 

 meteorologic phenomena is the rainbow-, which result* 

 from the decomposition of light by refraction through 

 drops of rain, and subsequent reflection. Ilainbows are 



